1. Field of the Invention
The present invention relates to mobile radio terminals such as, but not limited to, mobile radio terminals described by the 3GPP TS 25.211 3.7.0 (2001-06) Technical Specification which is incorporated herein by reference in its entirety.
2. Description of the Prior Art
As general background, the aforementioned 3GPP Technical Specification defines radio transmissions to mobile data receivers employing radio frames each having 15 slots. The length of each frame is 38,400 chips and each slot is 2,560 chips.
The common downlink physical channels in the Technical Specification include a common pilot channel (CPICH) which carries predefined bit/symbol sequences as described in Chapter 5.3.3.1. The CPICH channel may utilize two spatially diverse antennas which respectively transmit first and second complex sequences. The CPICH channel is transmitted from both antennas using the same channelization and scrambling code but, the predefined symbol sequence of each antenna is different.
FIG. 1 illustrates a diagram of the predefined symbol sequences of the CPICH channel for the antennas. Antenna 1 transmits a repeating sequence of symbols “A” and antenna 2 transmits a repeating sequence of alternating negative pairs of symbols “−A” and “A”. The symbols themselves are transmitted as first and second complex sequences. The spreading code utilized is 256 chips per bit.
The Technical Specification, while describing the use of spatial diverse antennas for transmitting the predefined symbol sequences for the CPICH channel, does not specify how the receiver processes the spatially diverse transmissions.
RAKE demodulators are well known. For example, see pages 842–851 of Digital Communications, 4th Edition, John P. Proakis, McGraw-Hill 2001, and the Assignee's U.S. patent application Ser. No. 09/915,382, filed Jul. 27, 2001, “Method and Apparatus for Synchronization” which are incorporated herein by reference in their entirety. A RAKE receiver detects at least one peak with multiple peaks representing reception of multipath components of the transmission. The fingers of the RAKE receiver are aligned in time with as many multipath components as possible so as to increase the signal level which is detected. The number of fingers in a RAKE receiver used for signal detection may be set up to a maximum number designed into the receiver. The number of fingers which are used corresponds to the number of peaks detected in the received transmissions up to the maximum number of fingers designed into the receiver.